1. Technical Field
The present invention relates to a method and device for forming parts and, more particularly, to forming and ejecting net shaped and near net shaped parts with curved or spiral teeth.
2. Discussion
Commonly used techniques for forming members having spiral or otherwise curved projections do not adequately address the manufacturing difficulties and costs associated therewith. For example, a variety of gear configurations, including gears having spiral shaped teeth such as hypoid, spiral bevel, spiral spur, and helical gears, are used in a multitude of industries to translate mechanical movement of components through shafts formed integral with or otherwise connected to the gears. These and similar gears are commonly formed through multiple step forging and machining processes that gradually refine the gear form and the relatively precise dimensions of the gear teeth.
It should be noted that the manufacturing difficulties discussed herein are encountered during the manufacture of members other than gears as well as during forming processes other than forging. Moreover, the difficulties specifically related to forging are encountered during hot, warm, and cold forging of members having spiral or otherwise curved protruding projections. For simplicity, references in this application to "gears" also refer to any formed member having spiral or curved protrusions. In the interest of consistency and simplicity, the term "forging" is used to represent all recognized techniques for forming spiral toothed members including the above-mentioned cold, warm, and hot forging as well as other forming processes such as casting, powdered metal processing, and the like.
Commonly, the forging of a gear includes the selection of a predetermined volume of material, an initial preforming step such as descaling or breaking down the selected volume into a pancake, secondary preforming of the pancake into a forging blank of a selected configuration such as a cone, with or without a stem, and a finish forging step wherein the forging blank is formed into the general shape of the finished part either with or without partially or completely formed teeth protruding from the cone. The aforementioned steps are performed in a generally recognized manner through the use of a variety of dies. The forged gear without teeth or with the partially formed teeth is then machined to remove excess material and to complete the gear, and particularly the gear teeth, within required tolerances.
Commonly available forging and machining techniques used to manufacture gears with spiral teeth, such as those identified above, require a significant and costly amount of machining away of the space between the teeth of the spiral gear from the cone shaped forged blank. This large amount of machining results primarily from an inability to remove a spiral shaped gear with more completely forged teeth from the die without deforming the teeth. The present invention reduces the need for post-forming machining by more effectively ejecting the part from the die and without deforming the teeth.
Specifically, the standard technique for ejecting or "knocking out" a forged part from a die is to vertically displace the part relative to the die. However, when a part with spiral projections is ejected in this fashion the forged spiral teeth of the part tend to contact the projections in the die that define the teeth. Any such contact subjects the part and the tooth projections to an undesirable load that tends not only to inhibit removal of the part but also to deform the teeth thereby resulting in an inaccurate part.
The problems associated with tooth deformation increases with the severity of the tooth angles and is particularly troublesome for teeth having an angle relative to the body of greater than about ten (10.degree.) degrees. Moreover, tooth deformation is more likely to occur for certain forming processes. For example, the ejector pressure, the pressure imparted on the teeth during ejection, generally causes greater deformation for hot and warm forged parts, e.g., parts forged at a temperature greater than about 1300.degree. F., than for cold forged parts.
The present invention provides a method and device for removing a part having spiral projections from a die in a manner that prevents deformation of the projections as well as other undesirable consequences of contact between the part and die during ejection. In accordance with the present invention, ejection of the part from the die is accomplished by rotating the part in addition to the previously recognized method of axial displacement. Accordingly, the present invention overcomes the manufacturing process disadvantages associated with previously recognized methods for removing a part having spiral projections from a die. The present invention also realizes the above benefit while allowing the teeth to be more completely formed in the forging process thereby reducing the extent of the more expensive machining operation. Finally, by the present invention, a spirally toothed member may be formed through forging to achieve more consistent grain flow thereby providing a stronger member than those requiring more extensive machining.